What Are Surge Watts? Starting vs Running Watts Explained
Surge wattsAlso called starting or peak watts
The brief burst of power a motor or compressor (a fridge, an AC, a pump) draws when it starts, well above what it uses while running.
- Height: power, in watts (W), how fast energy flows right now
- Area: energy, in watt-hours (Wh), power × time
At a glance
- Who needs it
- Appliances with a motor or compressor
- Rule of thumb
- Up to about three times the rated watts (USDA Forest Service)
- Fridge, measured
- Starting current typically three times running current (Sandia report)
- What to check
- The surge or peak rating of the station, inverter or generator
Electric motors draw much more power when they first start, says the USDA Forest Service’s guide to small generators, and the harder a motor is to start, the more it needs. Its rule of thumb is three times the rated wattage: a motor rated at 500 W needs 1.5 kW at startup.
How big is a fridge’s surge?
It varies, and the official figures we found don’t agree exactly. A 2018 Sandia National Laboratories student report says a conventional fridge’s starting current is typically three times its running current, and measured startup power up to 35% above the steady draw in its own tests. Treat “up to about three times” as a rule of thumb, not a number for your fridge.
What does it mean for a power station?
A station lists two output figures: continuous watts and surge (or peak) watts. The continuous rating has to cover everything running at once; the surge rating has to cover a compressor starting. The report notes many inverters have a surge rating meant for exactly this. Our power station sizer flags when your list includes a compressor. The safest check is the station maker’s own list of supported appliances.
Published by the Plugged Sun editorial team
Related terms
Sources
- Safe Use of Small Generators (Official document, USDA Forest Service, Missoula Technology and Development Center, 2006)
- Analysis of Refrigeration Units in Off Grid PV/Wind Hybrid Systems on Tribal Land (SAND2018-12534 R) (Source, Sandia National Laboratories (student report), 2018)